Lean burn operating engines utilize emission control devices coupled to the engine to store NOx while operating lean, and then to reduce stored NOx when the engine operates rich.
Various catalyst formulations have been proposed for increasing the NOx storage capacity of emission control devices.
However, the inventors here have recognized a disadvantage with such catalysts. In particular, these catalysts typically have a lower maximum temperature durability, and also provide reduce HC and CO conversion efficiency at higher temperatures. As such, these catalysts are typically located downstream of another catalyst, thereby exposing them to lower temperatures. However, by placing them downstream, this creates various problems related to inefficient purging (since all of the oxidants in the upstream catalyst must first be purged before the downstream catalyst can be purged).